Personally I started photography about a year ago from somewhat zero and I have found studying stuff from internet to be a great help, along with books and magazines. I've gathered here some websites that I've been using myself that I find beneficial or have found while trying to help other people and finding good links for them (I've been gathering these slowly during last year while learning myself). There are some basic guides and something a bit more advanced. Hope you can find something beneficial from here.
This list naturally doesn't contain all possible sites and might even miss some excellent site (please, if you know some good sites, inform me, perhaps I can republish this list later with updates) but the ones that I've read during last year and found useful. If you type "photography" to google, you'll be floaded with loads of sites, so this should narrow it down at least a bit. I've gathered these links from different locations. Part I have found myself and part are from photography-forum or other forums.
Don't know where to start, just got your first SLR? Just the really basic things, explained quick and dirty.
[link] Bernies Better Beginners Guide to Photography
Basic terms explained quickly with few photos.
[link] Beginners guide to photography.
Just some basics, good quick article about shutter and aperture.
[link] The Basics of Photography
Again really basics, explained with nice illustrations.
[link] Photo.net making photos
A guide to basics of photography from photo.net learning section.
[link] Digital Camera Help
Some different articles, also about post processing.
[link] CNet Digital SLR buying guide.
Want to buy a dSLR since all your friends have one and you just need one even though you don't know what it is? At least read this first. And remember that the camera doesn't take the photos, you do.
General photography links.
Basic tutorials covering some basics and wide variety of different photography categories.
Few different tricks and tips. Includes explanation of flashmeter from string (quite handy).
[link] Luminous Landscape
Different guides, includes perhaps a bit advanced guides. Landscape, nature and documentary photography.
[link] Digital photography school - composition
Basic rules of composition explained quickly with photos.
[link] Ken Rockwell
I really depated with myself if I would take this site to this list. But here is it anyway. I just warn everyone that you really shouldn't take these things literally or even read this site before you have a bit better understanding about photography. As someone in photography-forum said "Ken Rockwell is an idiot, don't listen to him".
[link] Cambridge in Colour
Excellent guides to several quite often overlooked areas of photography. Read at least about levels and curves.
[link] Digital Photography FAQ
Quite long FAQ. If you have a question, check this one first, then ask questions.
[link] Canon EOS Beginners' FAQ
You're a newbie and bought a Canon dSLR? Read this site! Might be useful even for some more experienced people.
Want to be in full control of lighting for your photos? Sites with guides for artificial lighting and studio shots.
[link] Photoflex lighting school
Excellent guide covering lots of different studio setups (people and objects).
[link] Lighting names
Portrait Lighting basic setups.
Excellent off-camera lighting site using flashguns. (also check Lighting 101 while in there)
[link] Planet Neil
Contains the best on-camera flashgun photography guide I've read, a must for everyone who is new to using flash.
[link] Lighting essentials
Several different portrait setups explained with diagrams and few videos too.
Exposure metering system called Zone system explained. Developed by Ansel Adams. I also would recommend reading the book "The Negative". It's a good exposure metering system if you really want to have control over the exposure in your photos.
[link] Wikipedia article
Quite good article about the system.
[link] Simplified zone system
Simple explanation of zone system. Should be enough at least to get you started.
[link] Digital zone system tutorial
A tutorial using Zone system on digital camera.
Some hate it, some like it (personally I'm in-between, sometimes I hate it, sometimes I like it). But it's here and here's few guides.
[link] Wikipedia article.
Don't know what HDR is? Then read this article first.
[link] HDR-Club links
Link list by HDR club here in dA.
[link] Camera filters
I always prefer filters over HDR. Here's one guide. If you like landscape photography, learn to use filters (or I'll find you and bite your ankle).
Other specific guides:
Other guides that go into specfic areas of photography. Something to read if you're interested and want to go a bit deeper.
[link] Professional Wedding Photography tips
Promised to photograph relatives wedding and you only have entry level dSLR and kit lens? Well, you're screwed and this site doesn't save you, but it's still good guide to wedding photography.
[link] Great Landscape Photography
Some landscape photography guides. My favourite category within photography.
Other misc links
[link] Dpreview glossary
A glossary of different terms related to photography. Loads of interesting terms explained. Knowing these propably won't make you better photographer but you'll sure sound like one.
A history of digital cameras. Some nice-to-know stuff. If you're really interested or again just want to sound like you know something about photography.
Got a problem and don't know where to ask help? Don't go for the Art Scene forum in dA forums, look for place where photographers hang out.
[link] dA photography forum.
Don't go to art scene -forum with photography questions, come here. It's where I can be found from.
[link] Dpreview forums
Quite active forums. Source for many (usually false) rumours of upcoming cameras and lenses.
[link] Luminous landscape forums
Luminous landscape forums, just like the title says.
Contains a forum aimed for, yes you guessed right, Nikon users.
Sites containing longer link lists than here. See if you can find anything more useful yourself.
[link] Photography Websites
[link] National Geographic Recommended Photography links
As titles says. I used to respect National Geographic untill they said that there are polar bears in Finland.
[link] DPReview links.
Links from DPReview
[link] Explain that stuff...
Some more links, quite a list here too.
[link] List of Photo Websites
Some more links.
[link] Post processing tutorials
Yes, you can use Photoshop for post-processing, it's not cheating. People saying it's cheating are either newbies who don't know much about photography or bitter arrogant old men who are dissapointed that there are lots of more talented young photographer than they are, and they'll get it all easier! So here's few post processing tutorials.
Not really learning guides, but since so many always ask "Is lens xx any good or would yy be better?". First try to read yourself.
Contains several quite nice lens reviews.
User reviews, lots of them.
[link] Lens Evaluations
Some Nikkor lens evaluations.
Again, not guides but still good idea to check these.
This site again? Well, it contains loads of detailed camera reviews. So if you're wondering that should you buy a certain camera, before asking, read the review if you can find it here.
[link] Imaging Resources
Haven't read myself that much but heard that it should be a good site.
[link] Steve Sanders
Again, reviews etc.
Well, there's my list. Hope you find some useful sites from this list.